My invention relates to a control circuit for a radio repeater, and particularly to such a control circuit for preventing a voice signal from interfering with an information tone signal when both signals are simultaneously transmitted by the repeater.
Radio repeaters are used to receive signals from a relatively weak transmitter and to re-transmit the same signals with a relatively strong transmitter. Some repeaters must re-transmit two received signals at the same time. An example of this may be found in an emergency medical repeater which receives voice signals on a first frequency and tone signals (indicative of medical information) on a second frequency, and re-transmits both signals on a third frequency. Typically, such a repeater is on an ambulance or emergency vehicle. The voice signals enable a doctor at a hospital to provide instructions, and the tone signals enable medical symptoms or information about a patient to be sent to the hospital for study. It is therefore very important or essential that the tone signals be transmitted accurately so that a sound diagnosis can be made from the information.
Accordingly a principal object of my invention is to provide a new and improved control circuit for a radio repeater.
Another and more specific object of my invention is to provide a new and improved control circuit that provides accurate repeater transmission of tone signals representing information.
In addition to the need for accurate tone signals, voice transmission is very desirable if not essential. Such voice transmission enables a doctor or medical expert to analyze the medical information transmitted by repeater tone signals, and to provide guidance or instructions for the person obtaining the medical information.
Accordingly, another and fairly specific object of my invention is to provide a new and improved radio repeater control circuit that prevents voice signals from interfering with information tone signals even though both signals are simultaneously repeated or re-transmitted together.
Prior circuits have dealt with the problem caused by voice signals interfering with tone information signals. One such circuit simply reduces the modulation levels of both the voice signals and the tone signals equally. While this circuit may prevent overmodulation of the repeater transmitter, it does not prevent the voice frequency signal from interfering with the information tone frequency signal, particularly when the voice frequency signal is stronger than the tone frequency signal.
Accordingly, another object of my invention is to provide a new and improved control circuit that improves the signal to noise ratio of information tone frequency signals.
Another object of my invention is to provide a new and improved control circuit that improves the signal to noise ratio of information tone frequency signals transmitted simultaneously with voice frequency signals, and that does not overload the transmitter modulator.